The present invention relates to radar systems, and more particularly to radar systems which reduce the effect of sea-clutter.
A radar target is detected by receiving radar energy of the transmitted radar beam which has been reflected back to the receiver by the target. When attempting to detect targets on the surface of the ocean, the waves also reflect the transmitted beam back to the receiver with varying amounts of success, causing what is commonly called sea-clutter. When waves cause particularly large reflection, it is termed a sea-spike. A sea-spike can appear as a target, and will occur randomly in time and location, lasting for approximately one-hundredth of a second.
The collective effect of radar reflection from the oceans's surface including that of sea-spikes is termed sea-clutter because it may cause a radar display to appear cluttered with false targets and distracting non-target radar returns. It is well known that sea-clutter has been a long felt problem causing interference with target detection and therefore resulting in degraded system performance.
Prior methods attempting to reduce the effect of sea-clutter have included techniques which either necessitate increased range and angular resolution of the radar, or which require utilization of scan-to-scan integration and rapidly rotating radar antennas. Increasing resolution of the radar by shortening the pulse-length, although fairly satisfactory in reducing the average value of the sea-clutter, does not significantly affect the magnitude of the sea-spikes, and they remain essentially unchanged.
Utilization of scan-to-scan integration in conjunction with a rapidly rotating radar antenna can reduce the magnitude of received sea-spikes somewhat but is not a satisfactory solution for two reasons: first, lengthy integration time is required to significantly reduce the magnitude of received sea-spikes, and secondly, the radar platform must be either motionless (very difficult for a ship in water) or be compensated for its motion. Compensation for motion is both difficult and expensive while lengthy integration times are generally quite unsatisfactory.
The present invention overcomes these difficulties. The radar antenna can be located on a moving platform without any compensation for motion being necessary. In addition, long objectionable integration time is also unnecessary.